The mining company seeking to build Minnesota's first hard-rock mine did not mislead the state about the size of the copper-nickel mine it intends to build, and its air permit "remains in effect," state pollution regulators said Monday.

The decision by the Minnesota Pollution Control Agency (MPCA) frees up the air pollution permit it issued for the PolyMet Mining Corp.'s proposed mine, but it does not clear the way for construction of the $1 billion Iron Range mine because other environmental disputes around the bitterly contested project remain unresolved.

Steps to open up northern Minnesota to hard-rock "nonferrous" mining — mining for materials other than iron ore — have been extremely divisive for the state. PolyMet's copper, nickel and platinum mine would provide jobs and metals central to a low-carbon economy, but the environmental costs are too high, environmental groups have long argued. Among other things, the open-pit mine would destroy more than 900 acres of wetlands on former Superior National Forest land south of Babbitt, and generate more than 200 million tons of polluted water to be stored behind a dam that would need to be indefinitely maintained.

It's one of two copper-nickel mines that foreign mining companies are pursuing in northern Minnesota. The other, known as Twin Metals, which Chilean mining company Antofagasta wants to build just outside the Boundary Waters Canoe Area Wilderness, also faces an uncertain future.

In the findings of fact out Monday, the MPCA said it "carefully evaluated" the evidence for a future PolyMet mine expansion and decided that doesn't change the agency's position that the company will abide by the permit it was issued.

"Even if they expanded they were required to come back and seek a new permit," MPCA spokesman Darin Broton said in an interview.

PolyMet seized the latest decision as a victory.

"As we have steadfastly maintained, the facts and science prove the project will meet air quality standards," PolyMet Chairman and CEO Jon Cherry said in a statement. "Of 22 lawsuits challenging the project, only four cases remain and those are planned to be heard during 2022."

St. Paul-based PolyMet is majority-owned by Glencore in Switzerland.

The Minnesota Center for Environmental Advocacy, one of a number of groups and Native American tribes opposed to the mine, said it's mulling another appeal.

"We are disappointed that the Minnesota Pollution Control Agency has once again failed to conduct a rigorous investigation into the facts surrounding the size and scale of PolyMet's true mining plans as shared with investors and securities regulators," said JT Haines, the Center's northeastern Minnesota program director.

PolyMet's air permit has traveled through the state courts, up to the Minnesota Supreme Court and back again to the Appeals Court. Earlier this year, the Appeals Court ordered the the MPCA to further review whether the company deceptively sought a less stringent permit for a mine operation smaller than the one it actually planned. That's called engaging in "sham permitting."

The air pollution permit limits the air emissions from PolyMet's proposed mine to 250 tons per year of any individual regulated air pollutant, such as particulate matter, sulfur dioxide and nitrogen oxide. A larger mine would likely require a stricter and more time-consuming air permit.

The air pollution permit does not regulate greenhouse gas emissions, but PolyMet's operation plant has the potential to emit 160,000 tons of greenhouse gases per year, MPCA documents show.